1. Field of the Invention
This invention relates to an auxiliary artificial heart of an embedded type, embedded in the left or right ventricle of the heart in a human body, and more particularly to an artificial heart operated at high reliability by preventing body fluids such as blood from adversely entering the artificial heart.
2. Description of the Related Art
Conventional artificial hearts are of the diaphragm type, sack type, axially symmetric type, centrifugal type, of pusher plate type or the like. Each of these conventional artificial hearts delivers blood in place of a human heart or by bypassing it.
Recently, an auxiliary artificial heart has been developed which is embedded in a ventricle of a human heart and has the tip end of a nozzle passing through an aorta valve or the like such that blood is delivered from the ventricle into an aorta through the nozzle. The artificial heart does not suppress any function of the human heart when it is installed in the human heart and it delivers additional blood into the aorta when blood pumped out from the human heart is insufficient. The blood is delivered not only by the artificial heart but also by the pulsing or beating of the human heart. Even if the operation of the artificial heart happens to stop, blood is delivered to the body by beating of the human heart.
Naturally, the volume of the part of the artificial heart which is inserted in a ventricle of the human heart must be smaller than the volume of the human heart when it is fully contracted. Such an artificial heart has a pump body comprising a cylindrical axial-flow pump section, a nozzle section provided on its distal end and a driving section provided on the proximal end of the axial-flow pump section. The cardiac apex of a ventricle of a human heart is cut and a short cylindrical cardiac apex ring is embedded therein. The pump section and the nozzle section are inserted in the ventricle through the cardiac apex ring, and the distal end of the nozzle section is inserted in an aorta through its aorta valve or the like. The driving section which has a large volume is embedded in a portion of the thorax which is outside of the human heart.
The artificial hearts has the following problem in connection with the function of a shaft-sealing mechanism provided between the pump section and the driving section. With the artificial heart, a motor and other elements are housed in the driving section, and the rotor of the pump section is driven via a driving shaft extending from the driving section to the pump section. Blood supplied by systemic blood pressure flows through the pump section. In this arrangement, blood is not allowed to enter the space in the driving section. If blood enters the space defined in the driving section, coagulation of blood occurs and the operation of the motor stops.
It is necessary to provide, between the driving section and the pump section, a sealing mechanism for sealing the driving shaft in a liquid tight state in order to prevent blood from entering the interior of the driving section. Since, however, the artificial heart is embedded in a human body, the artificial heart must be operated for a long time without maintenance. It is not easy with the present technology to provide a shaft-sealing mechanism with which perfect sealing is maintained for a long time.
The object of this invention is to provide an artificial heart which has a shaft-sealing mechanism for completely preventing blood from entering the interior of a driving section for a long time.
An auxiliary artificial heart according to this invention inserted in a ventricle of a human heart, including a cylindrical cardiac apex ring embedded in the cardiac apex of the human heart by cutting the cardiac apex, and a main body of the artificial heart comprising a cylindrical axial flow pump section inserted in the ventricle of the human heart through the cardiac apex ring, a nozzle section extending outward from the distal end of the pump section through the aorta valve of the human heart and a driving section provided on the proximal end of the pump section and disposed outside (or externally) of the human heart, for driving the pump section through a driving shaft.
Between the driving section and the pump section is provided a sealing mechanism for maintaining the driving shaft in a liquid tight state to prevent blood from entering the interior of the driving section from the pump section. The sealing mechanism defines a sealing liquid chamber surrounding the driving shaft at the driving section and a sealing liquid is filled in the sealing liquid chamber.
According to a preferred embodiment, the sealing liquid includes a physiological sodium chloride solution or an anticoagulant such as heparin, and the sealing liquid chamber communicates with a sealing liquid bag made of flexible material, filled with the sealing liquid and embedded in the human body.
The sealing mechanism is provided with an oil seal made of elastic material, closely fitted on the outer peripheral surface of the driving shaft due to its elastic deformation and forming a lubricating film of the sealing liquid between the peripheral surface of the driving shaft and the oil seal.
The pump section is driven by a motor or the like driving unit housed in the driving section. The pump section sucks blood from a ventricle of a human heart and discharges it into an aorta from the nozzle section of the distal end of the pump section by bypassing the aorta valve or the like. Thus, blood is delivered to the aorta not only by the beating of the human heart but also by means of the artificial heart. The artificial heart supplements any insufficient amount of blood which is not provided by the human heart, whereby it is ensured that the necessary amount of blood can be delivered. The volume of the pump section is smaller than the volume of the ventricle of the human heart when it contracts most so as not to interfere with natural beating of the human heart.
The sealing mechanism prevents blood from entering the driving section from the pump section. In this case, the sealing mechanism defines a sealing liquid chamber at the driving section, and a sealing liquid such as a physiological sodium chloride solution fills the sealing liquid chamber. Sealing and lubrication of the sealing mechanism are ensured by the sealing liquid, and blood is securely prevented from entering the interior of the driving section from the sealing mechanism.
Even if the sealing mechanism is deteriorated and blood enters the mechanism, the blood which has entered the mechanism is mixed with the sealing liquid. Thus, blood is not coagulated and does not prevent the smooth operation of the artificial heart.
In the embodiment, the sealing mechanism is provided with an oil seal which forms a lubricant film of the sealing liquid between the oil seal and the outer peripheral surface of the driving shaft and is elastically closely fitted on the outer peripheral surface of the driving shaft for securely preventing the entrance of blood such that the oil seal is not worn and is durable. The oil seal can be designed such that the lubricant film formed between the oil seal and the outer peripheral surface of the driving shaft delivers blood in only one direction toward the pump section. This structure prevents blood from entering the interior of the driving section.
According to the preferred embodiment, the sealing liquid chamber communicates with the sealing liquid bag embedded in the human thorax or other location. A sealing liquid is supplemented from the sealing liquid bag and thus can be supplied to the sealing liquid chamber for a long time.
In a preferred embodiment, the driving shaft uses a dynamic pressure bearing made of ceramic material operated in the sealing liquid. A coating film is formed between the sliding surfaces due to the dynamic pressure of the sealing liquid, thereby reducing rotational resistance of the bearing and preventing wear, leading to high reliability.
When the driving shaft is rotated, the dynamic pressure bearing generates dynamic pressure. The dynamic pressure provide a liquid seal between the sealing liquid chamber and the driving section. The sealing liquid is thereby prevented from flowing from the sealing liquid chamber into the driving section.
The dynamic pressure bearing, which is mounted on the distal end portion of the driving shaft, supplies the sealing liquid to the oil seal. Hence, the sealing liquid circulates in the artificial heart, preventing foreign bodies from depositing.
In a further preferred embodiment, a metal plating is formed on the outer peripheral surface of the driving shaft. Tetrafluoroethylene and its derivatives are made eutectic in the metal plating film, thereby improving not only lubricating properties between the driving shaft and the oil seal but also durability.
The metal plating film of this kind is water-repellent and is well compatible with the living body. Any component that contacts blood or other body fluid may be covered entirely with such a metal plating film.
Additional objects and advantages of the invention will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The objects and advantages of the invention may be realized and obtained by means of the instrumentalities and combinations particularly pointed out in the appended claims.